The American Medical Association (AMA) was formed in 1845 to gain for medical doctors a monopoly on legal licensure as health practitioners. The young AMA waged fierce (and quite successful) battles to de-certify the then-dominant natural healers — a range of herbalists, midwives, and homeopathic doctors […] By the early 20th century, the AMA had secured powerful big-coporation ^([sic]) backing for its plan to uniformize legal requirements to practice medicine in every state.
Source: wiktionary